The process of immunization involves antigen uptake and processing by professional antigen presenting cells (APCs), activation of APCs, and migration of antigen-bearing cells to lymphoid organs. This in turn can result in the activation of T lymphocytes. This process is dependent upon the presence of inflammatory signals usually provided by microbial pattern recognition. Previous work has shown that antibody molecules provide an ideal delivery vehicle for antigen presentation and vaccination. Antibodies can efficiently direct an associated antigen to a particular cellular subset, such as dendritic cells, and simultaneously fulfill the requirement for cellular activation. Depending on the type of dendritic subset targeted, a prediction is that a Th1 or Th2-1ike responses will result. In addition, by altering the molecular form of the antigenic Ig molecules, and specifying a target receptor, antigen may be directed into either the MHC class I or MHC class II antigen presentation pathways. This proposal describes experiments to establish the basic principles of antibody-directed antigen presentation leading to immunization. More importantly, the experiments will lead to the design of a new generation of vaccines capable of directing the class and thus the effectiveness of immune responses.